General Commands
connect <IP:Port>: Connects directly to a server.
disconnect: Disconnects from the current server.
exit or quit: Closes Steam.
clear: Clears the console screen.
Network Commands
net_status: Displays current network status.
net_graph <0/1/2/3>: Shows network graph details (0 = off, 1 = basic, 2 = more detailed).
net_start: Starts network debugging.
net_stop: Stops network debugging.
net_showudp: Shows all active UDP network connections.
net_showtcp: Shows all active TCP network connections.
Download and Update Commands
download_depot <AppID> <DepotID>: Downloads a specific depot for an app.
app_update <AppID>: Updates a specified game/app.
app_info_print <AppID>: Shows detailed app info.
app_config <AppID>: Displays configuration for an app.
app_installed <AppID>: Checks if an app is installed.
app_uninstall <AppID>: Uninstalls an app.
update_pause: Pauses all current updates.
update_resume: Resumes paused updates.
Debugging and Logging
log_ipc: Logs Inter-Process Communication.
log_net: Logs network activity.
log_voice: Logs voice communication.
log_assert <0/1>: Enables or disables assertion logging.
debug_dump: Dumps debugging information.
debug_info: Displays general debug info.
debug_window: Opens a window showing debug information.
error_report <AppID>: Reports an error for a specific app.
Game-Specific Commands
force_install_dir <directory>: Sets installation path for a game.
language <language>: Sets language for Steam or a game.
+clientport <port>: Sets client port (useful for NAT issues).
validate <AppID>: Validates game files.
reset_stats <AppID>: Resets achievements or stats for an app.
set_launch_option <option>: Sets a launch option for an app.
System Information
license_print: Displays Steam license info.
app_status <AppID>: Shows app status.
ping: Tests Steam's connection latency.
sys_info: Prints system information.
cpu_usage: Displays CPU usage.
memory_usage: Shows memory usage stats.
disk_usage: Displays disk usage.
gpu_info: Shows GPU information and status.
Friend Commands
friends: Displays the friends list.
msg <SteamID> <message>: Sends a message to a friend.
friend_request <SteamID>: Sends a friend request to the specified SteamID.
block_user <SteamID>: Blocks a user by SteamID.
unblock_user <SteamID>: Unblocks a user.
friend_list_online: Lists friends who are online.
friend_list_offline: Lists friends who are offline.
Game Launch Options
Set these in the Launch Options box:

-novid: Skips intro video.
-windowed: Starts in windowed mode.
-fullscreen: Starts in fullscreen mode.
-w <width> -h <height>: Sets screen resolution.
-console: Enables in-game console.
+sv_cheats 1: Enables cheats (for supported games).
+fps_max <value>: Sets max frame rate.
-safe: Starts the game in safe mode.
+mat_dxlevel <version>: Forces a DirectX level.
Hidden Advanced Options (may not work in all games)
+developer <0/1>: Enables developer mode.
+cl_showfps <0/1>: Shows FPS (frames per second).
-nojoy: Disables joystick support.
-high: Sets the game process priority to high.
-threads <num>: Sets the number of threads used by the game.
+exec <filename>: Executes a config file on launch.
In-Game Commands (specific to Valve games)
killserver: Stops a server.
retry: Reconnects to the last server.
status: Displays server and player information.
version: Shows game version.
+alias <command>: Sets an alias for a command.
-console: Disables in-game console.
sensitivity <value>: Sets mouse sensitivity.
volume <value>: Sets in-game volume.
Voice and Audio Commands
voice_enable <0/1>: Enables or disables voice chat.
voice_loopback <0/1>: Enables voice loopback.
voice_threshold <value>: Sets the voice activation threshold.
snd_restart: Restarts sound system.
snd_mixahead <value>: Adjusts sound latency.
volume <value>: Sets master volume level.
snd_surround <0/1>: Enables surround sound.
Client Configurations and Settings
steam_restart: Restarts Steam.
steam_log: Shows the Steam client log.
steam_settings: Opens Steam client settings.
steam_notification <0/1>: Toggles notifications.
steam_password <newpassword>: Changes your Steam password.
steam_guard: Manages Steam Guard settings.